Circuit arrangement for detecting a type for a solenoid valve

ABSTRACT

A circuit arrangement for detecting a solenoid valve type in vehicles, including at least one solenoid valve in the circuit arrangement for detecting the solenoid valve type and having at least one coil winding having a resistance of the typical order of magnitude for a predetermined vehicle electrical distribution system supply voltage, a constant current source, arranged to impress a predetermined measurement current into the one coil winding of the solenoid valve, a current mirror circuit, arranged to generate a second voltage on a detection section of the circuit arrangement from a first voltage produced as a result of the impressed measurement current on the at least one coil winding of the at least one solenoid valve, in which the second voltage produced on the detection section is passed out, on the detection section, directly to a microcontroller in a control device for determining the type of solenoid valve.

FIELD OF THE INVENTION

The present invention relates to a circuit arrangement for detecting atype of solenoid valve and relates in particular to a circuitarrangement for detecting the type of solenoid valves installed in avehicle in respect of whether the configuration of said solenoid valvesis suitable for an existing vehicle electrical distribution systemvoltage range.

BACKGROUND INFORMATION

In automotive engineering, in particular in the case of utilityvehicles, vehicle electrical distribution systems having two differentvehicle electrical distribution system voltages are conventional.Primarily, these are vehicle electrical distribution systems with arated voltage of 12 V and vehicle electrical distribution systems with arated voltage of 24 V. For both of these voltage ranges, normallysolenoid valves are used whose coils differ from one another in terms oftheir resistance.

For manufacturers of utility vehicles which produce vehicles with bothvehicle electrical distribution system variants, it may arise thatsolenoid valves for 12 V are incorrectly installed in vehicles with avehicle electrical distribution system of 24 V or solenoid valves for 24V are incorrectly installed in vehicles with a vehicle electricaldistribution system of 12 V.

Previous anti-lock braking system or ABS control devices for utilityvehicles in the vicinity of which solenoid valves under consideration inparticular here are used have not been able to identify such faults,with the result that, in the case of solenoid valves for 24 V in a 12 Vvehicle electrical distribution system, it may firstly arise thatnecessary valve activations do not take place and, secondly, in a caseof solenoid valves for 12 V in a 24 V vehicle electrical distributionsystem, overload of the solenoid valves owing to excessively highcurrents can occur, which results in failure of said solenoid valves.

The fundamental reason for this consists in that previous configurationsof ABS systems monitor end states of solenoid valves only for shortcircuits to ground, short circuits to the vehicle electricaldistribution system supply voltage or battery voltage and/or for loadinterruptions. Identification of a fault in this case generally takesplace by evaluation of voltage feedback. High-resistance loads are inthis case only identified above very high resistance values, however.

Against this background, the invention is based on the object ofproviding a circuit arrangement for improved detection of a type ofsolenoid valve, with which the type of solenoid valve installed in anelectrical distribution system of a vehicle can be determined in respectof corresponding voltage range of solenoid valve and vehicle electricaldistribution system in the case of low resistance values to beconsidered.

In accordance with the invention, this object is achieved by thefeatures described herein. Advantageous developments of the inventionare the subject matter of the attached dependent claims.

The invention is based on the general concept of detecting a solenoidvalve which has been incorrectly installed in a vehicle, in particular autility vehicle, i.e. a solenoid valve whose voltage range does notmatch the voltage range of the electrical distribution system of thevehicle in which it is installed, via the resistance of the coilsprovided in each case in the solenoid valves of different voltageranges. While coils of solenoid valves configured for 24 V, for example24 V pressure control solenoid valves, have a resistance of typicallyapproximately 16 ohms, for example, coils of solenoid valves configuredfor 12 V, for example, have a resistance of typically approximately 5ohms. If a low measurement current is now impressed into each of thecoils provided, the voltage resulting from this can be measured at thesolenoid valve coil and evaluated via a microcontroller in acorresponding control device for determining the voltage rating range ofthe solenoid valve. The resistance of the solenoid valve coils can becalculated and determined from the measured voltage and the knownimpressed current.

In accordance with this general concept of the invention, the proposedcircuit arrangement is advantageous insofar as the measurement circuitcan be kept simple at low cost, but nevertheless provides measurementaccuracy with a corresponding configuration such that it is possible tosafely distinguish between at least two coil types over a specifiedvoltage range, temperature range and tolerance range. A furtheradvantage consists in that the configuration of the circuit arrangementis possible in such a way that even low impressed currents aresufficient for the coil type determination without any restriction tothe actual level of a vehicle electrical distribution system ratedvoltage, with the result that the detection of the coil type is possiblewithout electrically and/or mechanically activating the associatedsolenoid valve. The coil type determination can therefore take place insystem-transparent fashion and as such in a manner which has no effecton remaining functions of the basic ABS system, for example, in otherwords without the ABS system being impaired or disrupted in any way.

The object is therefore achieved by a circuit arrangement for detectinga type of solenoid valve in vehicles, characterized by at least onesolenoid valve which is incorporated into the circuit arrangement forthe purpose of detecting the type of said solenoid valve and has atleast one coil winding having a resistance which is of the typical orderof magnitude for a predetermined vehicle electrical distribution systemsupply voltage; a constant current source, which is arranged so as toimpress a predetermined measurement current into the at least one coilwinding of the at least one solenoid valve; a current mirror circuit,which is arranged so as to generate a second voltage on a detectionsection of the circuit arrangement from a first voltage produced as aresult of the impressed measurement current on the at least one coilwinding of the at least one solenoid valve; wherein the second voltageproduced on the detection section is passed out, on the detectionsection, directly to a microcontroller in a control device fordetermining the type of solenoid valve.

As a result, reliable identification of an operating voltage of asolenoid valve can be performed by a simple and inexpensive circuitconfiguration, which can also be integrated in an already existingcontrol device or solenoid valve module, or can be configured as anadditional module, wherein the identification only needs to be performedonce during or after initialization of the remaining controlelectronics, and the identification in this case still remains withoutany functional effect on a respectively measured solenoid valve andtherefore does not result in any further actuation or activation of thesolenoid valve or other components in its range of action. In addition,a suitable configuration of the circuit configuration also enables aresistance measurement to ground potential, and a defective coil windingcan also be determined via this resistance measurement, for example whenthe expected typical resistance value can no longer be determined, andalso the temperature or change in temperature of the coil turn can bedetected by such a resistance measurement.

The detected type of solenoid valve may be a vehicle electricaldistribution system supply voltage for which the solenoid valve isconfigured, wherein the vehicle electrical distribution system supplyvoltage includes rated voltages of 12 V and/or 24 V and/or more than 24V, and the solenoid valve is a pressure control solenoid valve for usein braking systems and/or traction control systems for a utilityvehicle.

As a result, it is possible to conclude that there is a correct systemstate in safety-relevant parts of a utility vehicle in a quick andexpedient manner by distinguishing between two possible variants anddetermining whether there is a faulty installation, for example afterthe manufacturer's production facility or else after time in a workshop,which can result in a non-response of a solenoid valve and/or in failureof a solenoid valve.

If the order of magnitude of the resistance of the coil winding of thesolenoid valve for a rated voltage of 12 V is typically within asingle-digit resistance range and, for a higher rated voltagedistinguishable therefrom, is typically in a two-digit to three-digitresistance range, safe and nevertheless activation-less detection withinthe scope of the orders of magnitude of other system signals ispossible.

The constant current source may include a transistor, which is connectedto a respective resistance at the emitter, base and collector, with avoltage signal which is 5 V in the measurement state of the circuitarrangement being applied to the base connection of said transistor.

Further, the measurement current impressed by the constant currentsource into the at least one coil winding of the at least one solenoidvalve may be configured such that solenoid valve type detection isreliably possible, but the flow of said measurement current does not yetresult in functional activation of a respectively measured solenoidvalve, and the measurement current is approximately 9 mA.

As a result, it is possible to generate and impress a suitablemeasurement current with a simple configuration and utilization ofvoltage potentials present in the entire system.

The current mirror circuit may include an operational amplifier, whoseinput voltage range up to its supply voltage is sufficient, a transistorand a second resistance, which forms the detection section, and thecurrent mirror circuit transmits the first voltage to a firstresistance, which is connected to the transistor towards the vehicleelectrical distribution system supply voltage.

This arrangement makes it possible in a simple manner to transmit thevoltage produced by the impressed measurement current at the coil of ameasured solenoid valve to a circuit section on which said voltage canbe received and evaluated by a microcontroller. Particular advantagesresult from the fact that a voltage produced at external points, forexample on solenoid valves installed in wheel modules, can be convertedin a suitable manner into an internal detection voltage, and this canadditionally be matched to existing requirements by virtue of theconfiguration of the current mirror.

Advantageously, at least one first high-side switch for activating thecoil of the at least one solenoid valve is provided in series with theat least one solenoid valve, a second switch, which is common for the atleast one solenoid valve, is provided in parallel with the constantcurrent source to ground potential, wherein said second switch is closedin the normal operating state, and a third switch for switchablyimpressing the constant current is provided at the constant currentsource, wherein, in a measurement operation state, the third switch isclosed, the second switch is open, and the at least one first switch isclosed.

This arrangement makes it possible, when a plurality of solenoid valvesare provided, to implement and evaluate a separate and/or sequentialmeasurement of individual solenoid valves by defined setting of theswitching states of the individual switches by virtue of, for example,first the second and third switches being set to a state intended forthe measurement and then the first switches which, in the case of aplurality of solenoid valves, are present in total as a plurality but ineach case with only one on each individual solenoid valve being switchedon/off or turned on successively, and therefore the impressedmeasurement current flowing in each case only through a or the desiredcoil(s) of the solenoid valves to be measured.

A sensitivity and/or a detection range of the circuit arrangement may beadjustable, wherein the resistance of the solenoid coils can becalculated via the transformation ratio U1/U2 of the first voltage tothe second voltage and the impressed measurement current.

If the sensitivity and/or the detection range of the circuit arrangementis adjustable or capable of being switched over, it becomes possible toinfluence and possibly match the accuracy of the measurement and/or, ifnecessary, to measure a relatively large resistance difference betweenthe resistance values of individual solenoid valve coils. Firstly, thecircuit arrangement becomes suitable for universal use thereby, andsecondly it becomes possible to replace individual solenoid valves with,for example, valves of another, for example newer, type with differentcoil resistance values without needing to make any changes to theremaining circuit arrangement. Since, in addition, the first voltagegenerated by the impressed measurement current or the value thereofconverted after mirroring is detectable and the impressed measurementcurrent itself is known, this enables a coil resistance detectionwithout any notable loading of the system in respect of time andcomputation complexity.

The circuit arrangement may form part of an anti-lock braking systemand/or part of a traction control system for utility vehicles.

In such safety-relevant sections of vehicles, the integration of anadditional identification, in accordance with the invention, of thepresence of a solenoid valve with the correct rating in respect of thevehicle electrical distribution system supply voltage is particularlyadvantageous because, for example, even in the case of system activationduring end-of-line testing in the manufacturer's factory or oncemaintenance or repair work has been performed, for example, it ispossible to avoid, by suitable signaling, a situation whereby a vehiclewith parts which are unsuitable for operation at least initially is usedon the road again. In other words, the risk of a fault owing to a) anon-response of a solenoid valve as a result of a lack of drivabilityand/or b) a partial system failure as a result of destruction of asolenoid valve after operation outside its specification and/oroverloading becoming the responsibility of a driver of the utilityvehicle is effectively reduced.

Specifically, overall the circuit arrangement according to the inventionis in principle characterized by the fact that a battery is provided asvehicle electrical distribution system supply voltage, a firstresistance and at least one first switch are connected at in each caseone first connection to a high potential of the vehicle electricaldistribution system supply voltage, a transistor is connected at anemitter connection to the first resistance, an operational amplifier isconnected at an output thereof to a base connection of the transistor,an inverting input of the operational amplifier is connected to thefirst resistance and to the emitter connection of the transistor, anoninverting input of the operational amplifier is connected to a firstconnection of a second switch, a first connection of a third switch, anda second connection of the at least one solenoid valve, a firstconnection of the at least one solenoid valve is connected to a secondconnection of the at least one first switch, a collector connection ofthe transistor is connected to a first connection of a secondresistance, a second connection of the third switch is connected to afirst connection of the constant current source, and in each case asecond connection of the second resistance, a second connection of theconstant current source, and a second connection of the second switchare connected to a low potential of the vehicle electrical distributionsystem supply voltage, wherein the second voltage as measurement voltageis passed out to the microcontroller between the first connection of thesecond resistance and the collector connection of the transistor.

The invention will be described in more detail below using a exemplaryembodiment of the circuit arrangement with reference to the drawing.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows a simplified illustration of a circuit arrangement fordetecting the type of solenoid valve in accordance with an exemplaryembodiment.

DETAILED DESCRIPTION

As shown in the FIGURE, a vehicle electrical distribution system supplyvoltage for a vehicle, for example a utility vehicle, is provided. Thevehicle electrical distribution system supply voltage may be, forexample, a battery which provides a supply or battery voltage UB of 12 Vor 24 V. The vehicle electrical distribution system voltage supply isnot restricted to these voltages, however. Instead, the circuitarrangement, with a corresponding configuration, is suitable for anydesired vehicle electrical distribution system voltage supplies or anydesired vehicle electrical distribution system rated voltages, forexample even for those with supply or battery voltages of more than 24V, such as 42 V or the like. A first connection of a first resistanceR1, a first connection of a first switch S1 and a first connection of asecond switch S2 are connected to the positive potential of the vehicleelectrical distribution system voltage supply in the exemplaryembodiment shown. The second switch S2 may be in the form of a single ordouble field-effect transistor.

A second connection of the first resistance R1 is connected to anemitter connection of a transistor T1. As illustrated, the transistor T1is a PNP transistor, for example, but is not restricted thereto. Thecollector connection of the transistor T1 is connected to a firstconnection of a second resistance R2. The base connection of thetransistor T1 is connected to an output of an operational amplifier OP1,with the potential at the second connection of the first resistance R1being supplied to the inverting input connection of said operationalamplifier OP1. The operational amplifier OP1 is in this case may be onewhich has an input voltage range which reaches up to its supply voltage.

The noninverting connection of the operational amplifier OP1 isconnected to a first connection of a third switch S3. A first connectionof a current source I1 is connected to a second connection of the thirdswitch S3, said current source in turn being connected to groundpotential at a second connection.

The first connection of the third switch S3 is connected to the samepotential as a second connection of a first solenoid valve coil PCV1, asecond connection of a second solenoid valve coil PCV2 and a firstconnection of a fourth switch S4. A second connection of the fourthswitch S4 is connected to ground potential, and a first connection ofthe first solenoid valve coil PCV1 and a first connection of the secondsolenoid valve coil PCV2 are each connected to a second connection ofthe first switch S1 and a second connection of the second switch S2.

Although two series circuits comprising switches S1, S2 and solenoidvalve coils PCV1, PCV2 are shown in the FIGURE, said series circuits aremerely representative of any desired number of solenoid valve coilsPCV1, PCV2, . . . , PCVx which are possible with correspondinginterconnection with switches S1, S2, . . . , Sx, as is indicated by thecontinuing broken lines in the FIGURE.

In a practical configuration and/or modification of the circuitarrangement illustrated in simplified form in the FIGURE, the fourthswitch S4 is a switch to ground potential which is common to all of thesolenoid valve coils and is closed in a normal operating state. Inaddition, the first switch S1 and the second switch S2 are embodied asso-called high-side switches and may be embodied as high-side transistorswitches or high-side field-effect transistors, which as such areconnected to the positive supply potential and are not referred toground potential, but switch to the positive supply potential. The firstswitch S1 and the second switch S2 are arranged so as to activate thesolenoid valve coils PCV1 and PCV2 during intervention for regulation.

Since, as described above, high-side switches are used for activatingthe individual solenoid valve coils PCV1, PCV2, . . . , PCVx, thevoltage to be detected for determining the resistance of the solenoidvalve coils PCV1, PCV2, . . . , PCVx needs to be measured against thevehicle electrical distribution system supply voltage UB and transmittedin a suitable manner to the microcontroller (not shown), which is atground potential. It should be noted that the measurement can of coursealso be performed accordingly with respect to ground potential.

The current source I1 forms a constant current source and is arranged soas to impress the measurement current into the solenoid valve coilsPCV1, PCV2, . . . , PCVx via closing of the third switch S3 (and of thefirst switch S1 or the second switch S2). For this purpose, inaccordance with the exemplary embodiment, current source switching forimpressing a constant current as measurement current is used (in otherwords the measurement is performed by impressing a constant current) insuch a way that the measured voltage U1 at the respective solenoid valvecoil PCV1, PCV2, . . . , PCVx is independent of the level of the batteryor vehicle electrical distribution system supply voltage. Specifically,the current source I1 can include a transistor, for example an NPNtransistor or FET, which is connected at the base, emitter and collectorin each case to a suitable resistance, with a voltage of 5 V present atthe base connection of the transistor in the measurement state.

The current source I1 may be configured such that, in the exemplaryembodiment under consideration here, in order to distinguish betweensolenoid valve coils for vehicle electrical distribution system ratedvoltages of 12 V or 24 V and typical coil resistances of 5 ohms, i.e. avalue in a single-digit resistance range, or approximately 16 ohms, i.e.a value in a two-digit resistance range, it generates a constantmeasurement current of approximately 9 Ma given these two vehicleelectrical distribution system supply voltages, which constantmeasurement current is sufficient in magnitude to safely distinguish thetype of solenoid valve coil measured (its rated voltage) but still doesnot result in activation of the solenoid valve coil.

It goes without saying that, for other vehicle electrical distributionsystem rated voltages or for solenoid valves with a differentconfiguration or another intended use, for example pressure controlsolenoid valves for traction control systems or TCS, which at presentcan have, for example, a coil resistance of the order of magnitude ofbetween 8 ohms, i.e. a value in a single-digit resistance range, and 128ohms, i.e. a value in a three-digit resistance range, the circuitarrangement can be configured for identification of and distinguishingbetween such solenoid valves overall as well and therefore also forcorrespondingly other resistance values to be measured and/or constantmeasurement currents.

The operational amplifier OP1, the transistor T1 and the secondresistance R2 form a current mirror circuit, which mirrors or transmitsthe voltage U1 that can be measured at the parallel series circuits ofswitches S1, S2, . . . , Sx and solenoid valve coils PCV1, PCV2, . . . ,PCVx initially onto the first resistance R1 and then as voltage U2 ontothe second resistance R2. As illustrated schematically in the FIGURE byan arrow denoted by μC, the voltage U2 is passed out directly to themicrocontroller between the first connection of the second resistance R2and the collector connection of the transistor T1.

The measurement of the resistances of the solenoid valve coils PCV1,PCV2, . . . , PCVx advantageously only needs to be performed once, forexample during or after a switch-on operation of the control device.

In order to perform such a resistance measurement of the solenoid valvecoils PCV1, PCV2, . . . , PCVx for detection of the (voltage) typethereof, the second switch S2 is opened, the third switch S3 is closedand all of the switches S1, S2, . . . , Sx assigned in each case to theindividual solenoid valve coils PCV1, PCV2, . . . , PCVx are closedsuccessively. The resistance of the individual solenoid valve coilsPCV1, PCV2, . . . , PCVx can be determined or calculated via the voltagetransformation ratio U1/U2 known within the circuit arrangement and thelikewise known impressed measurement current from the current source I1if the saturation voltage as a voltage drop across the switches S1, S2,. . . , Sx is sufficiently low or else is known.

In addition, provision may be made for the circuit arrangement to beconfigured so as to be adjustable or capable of being switched over inrespect of sensitivity and/or detection range in such a way that moreprecise measurement is possible and/or larger and/or extended resistanceranges are measurable. Such a capacity for adjustment or switchover canbe achieved, for example, by virtue of the fact that the constantcurrent generated by the constant current source I1 is configured so asto be controllably variable in terms of its absolute magnitude, at leastone element of the current mirror circuit is configured so as to becontrollably variable, and/or the second resistance R2 is configured soas to be variably controllable, for example in accordance with a type ofresistance matrix comprising a plurality of resistances which areparallel to one another and are individually switchable via resistiveswitches in their feed lines. Depending on a point of action of theadjustability or capacity for switchover, in this case a change can becontrolled via the microcontroller by software, for example, or can beinitiated correspondingly by permanently wired adjustment points. Ingeneral, there is no restriction to a specific configuration embodimentof the adjustability or capacity for switchover as long as, by aspecific embodiment, the voltage transformation ratio U1/U2 known withinthe circuit arrangement and/or the likewise known impressed measurementcurrent from the current source I1 are influenced in a suitable mannerfor determining or calculating the resistance of the individual solenoidvalve coils PCV1, PCV2, . . . , PCVx so as to improve the measurementaccuracy or extend the measurement range.

It is noted that additionally also a defect in a coil winding, such as aturn-to-turn fault, for example, can be detected via the measurement ofthe resistance of the solenoid valve coils PCV1, PCV2, . . . , PCVx(i.e. the resistance measurement) described herein. Conclusions in thisregard can be drawn, for example, in the evaluating microcontrollerwhen, for example, a typical resistance value to be expected is nolonger present or determinable. In addition, in principle a temperatureand/or a change in temperature of a winding of a solenoid valve coilis/are also detectable by such a resistance measurement.

It goes without saying that the above-described exemplary embodiment isnot restricted to the elements specified by way of example and specificcircuitry forms, but rather that individual or else a plurality ofelements can be represented by functionally identical elements, circuitsof a plurality of elements, embodiments, in particular also in the caseof polarity reversal and/or the use of other types of line and/orembodiments of respectively used electronic switch types. It likewisegoes without saying that the resistance detection described herein forsolenoid valve coils is not restricted to solenoid valves in an ABSsystem or a TCS, but can be implemented in the case of a multiplicity ofother arrangements and systems, even those which are not only invehicles or utility vehicles, which meet the basic requirements for sucha resistance measurement and enable direct measurement of (impressed)valve currents in solenoid valve coils.

Such modifications, which are comparable or equivalent to the abovedetailed description of an exemplary embodiment, and likewise furthercircuit elements which can form further circuitry for suitablefunctional matching, adjustment and/or configuration, are not essentialto the functional principle of the circuit arrangement according to theinvention, however, and the specific selection of such modificationswill readily be inferred by a person skilled in the art and shouldtherefore not be considered as departing from the subject matter of theinvention or leaving the scope of protection of the invention inaccordance with the attached patent claims.

1-10. (canceled)
 11. A circuit arrangement for detecting a type of solenoid valve in a vehicle, comprising: at least one solenoid valve incorporated into the circuit arrangement to detect the type of the solenoid valve and having at least one coil winding having a resistance which is of the typical order of magnitude for a predetermined vehicle electrical distribution system supply voltage; a constant current source arranged so as to impress a predetermined measurement current into the at least one coil winding of the at least one solenoid valve; and a current mirror circuit arranged so as to generate a second voltage on a detection section of the circuit arrangement from a first voltage produced as a result of the impressed measurement current on the at least one coil winding of the at least one solenoid valve; wherein the second voltage produced on the detection section is passed out, on the detection section, directly to a microcontroller in a control device for determining the type of solenoid valve.
 12. The circuit arrangement of claim 11, wherein the detected type of solenoid valve is a vehicle electrical distribution system supply voltage for which the solenoid valve is designed, wherein the vehicle electrical distribution system supply voltage includes rated voltages of 12 V and/or 24 V, and in that the solenoid valve is a pressure control solenoid valve for use in braking systems and/or traction control systems of a utility vehicle.
 13. The circuit arrangement of claim 12, wherein the order of magnitude of the resistance of the coil winding of the solenoid valve for a rated voltage of 12 V is typically within a single-digit resistance value range, and for a higher rated voltage, is typically within a two-digit to three-digit resistance value range.
 14. The circuit arrangement of claim 11, wherein the constant current source includes a transistor, which is connected to a respective resistance at the emitter, base and collector, with a voltage signal which is 5 V in the measurement state of the circuit arrangement being applied to the base connection of said transistor.
 15. The circuit arrangement of claim 11, wherein the measurement current impressed by the constant current source into the at least one coil winding of the at least one solenoid valve is configured so that solenoid valve type detection is reliably possible, but the flow of said measurement current does not yet result in functional activation of a respectively measured solenoid valve, and the measurement current is approximately 9 mA.
 16. The circuit arrangement of claim 11, wherein the current mirror circuit includes an operational amplifier, whose input voltage range up to its supply voltage is sufficient, a transistor and a second resistance, which forms the detection section, and the current mirror circuit transmits the first voltage to a first resistance, which is connected to the transistor towards the vehicle electrical distribution system supply voltage.
 17. The circuit arrangement of claim 11, wherein at least one first high-side switch for activating the coil of the at least one solenoid valve is in series with the at least one solenoid valve, a second switch, which is common for the at least one solenoid valve, is in parallel with the constant current source to ground potential, wherein said second switch is closed in the normal operating state, and a third switch for switchably impressing the constant current is at the constant current source, and wherein, in a measurement operation state, the third switch is closed, the second switch is open, and the at least one first switch is closed.
 18. The circuit arrangement of claim 11, wherein a sensitivity and/or a detection range of the circuit arrangement is adjustable, wherein the resistance of the solenoid coils can be calculated via the transformation ratio of the first voltage to the second voltage and the impressed measurement current.
 19. The circuit arrangement of claim 11, wherein the circuit arrangement forms part of an anti-lock braking system and/or part of a traction control system for a utility vehicle.
 20. The circuit arrangement of claim 11, wherein a battery is provided as a vehicle electrical distribution system supply voltage, a first resistance and at least one first switch are connected at in each case one first connection to a high potential of the vehicle electrical distribution system supply voltage, a transistor is connected at an emitter connection to the first resistance, an operational amplifier is connected at an output thereof to a base connection of the transistor, an inverting input of the operational amplifier is connected to the first resistance and to the emitter connection of the transistor, a noninverting input of the operational amplifier is connected to a first connection of a second switch, a first connection of a third switch, and a second connection of the at least one solenoid valve, a first connection of the at least one solenoid valve is connected to a second connection of the at least one first switch, a collector connection of the transistor is connected to a first connection of a second resistance, a second connection of the third switch is connected to a first connection of the constant current source, and in each case a second connection of the second resistance, a second connection of the constant current source, and a second connection of the second switch are connected to a low potential of the vehicle electrical distribution system supply voltage, wherein the second voltage as measurement voltage is passed out to the microcontroller between the first connection of the second resistance and the collector connection of the transistor.
 21. The circuit arrangement of claim 11, wherein the detected type of solenoid valve is a vehicle electrical distribution system supply voltage for which the solenoid valve is designed, wherein the vehicle electrical distribution system supply voltage includes rated voltages of more than 24 V, and in that the solenoid valve is a pressure control solenoid valve for use in braking systems and/or traction control systems of a utility vehicle. 